Electronic structure of low-spin ferric chlorins: Characterization of bis(1-methylimidazole)(meso-tetraphenylchlorinato)iron(III) triflate

Article abstract of DOI:10.1039/b204006a

The synthesis and characterization of the trifluoromethanesulfonato derivative of bis(1-methylimidazole)tetrakis-(phenyl)chlorinatoiron(III) [Fe(TPC)(1-MeIm)₂]CF₃SO₃ 1 are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(2), 2.016 (6) A and to the pyrrole trans to it N(4), 2.032 (5) A are longer than the remaining two nitrogens: N(1), 2.005 (6) A and N(3), 1.972 (6) A leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The two axial ligand planes are parallel. The ¹H NMR isotropic shifts at 20°C of the different pyrrole protons of 1 varied from -8.6 ppm to -42.6 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(1-MeIm)₂]CF₃SO₃ 1 in solution is rhombic and shows the principal g-values g₁ = 2.47,g₂ = 2.42 and g₃ = 1.78 (Σg² = 15.1). These spectroscopic observations are indicative of a metal-based electron in the dπ orbital for the [Fe(TPC)(1-MeIm)₂]CF₃SO₃ (1) complex with a (d_xy)² (d_xzd_yz)³ ground state at any temperature.

Full text of DOI:10.1039/b204006a

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Electronic structure of low-spin ferric chlorins: characterization of
bis(1-methylimidazole)(meso-tetraphenylchlorinato)iron(III) triflate
Gérard Simonneaux,*a Marwan Kobeissia and Loïc Toupetb
a Laboratoire de Chimie Organométallique et Biologique, Université de Rennes 1,
UMR CNRS 6509, 35042 Rennes cedex, France. E-mail: simonnea@univ-rennes1.fr
b Groupe de Physique Cristalline, Université de Rennes 1, UA CNRS 040804,
Campus de Beaulieu, 35042 Rennes Cedex, France
Received 24th April 2002, Accepted 25th September 2002
First published as an Advance Article on the web 9th October 2002
The synthesis and characterization of the trifluoromethanesulfonato derivative of bis(1-methylimidazole)tetrakis-
(phenyl)chlorinatoiron() [Fe(TPC)(1-MeIm)2]CF3SO3 1 are reported. The crystal structure of complex 1 has
been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal–nitrogen
distances to the reduced pyrrole N(2), 2.016 (6) Å and to the pyrrole trans to it N(4), 2.032 (5) Å are longer than the
remaining two nitrogens: N(1), 2.005 (6) Å and N(3), 1.972 (6) Å leading to a core-hole expansion of the macrocycle
due to the reduced pyrrole. The two axial ligand planes are parallel. The 1H NMR isotropic shifts at 20 ЊC of the
different pyrrole protons of 1 varied from Ϫ8.6 ppm to Ϫ42.6 ppm according to bis-ligated complexes of low-spin
ferric chlorins. The EPR spectrum of [Fe(TPC)(1-MeIm)2]CF3SO3 1 in solution is rhombic and shows the principal
g-values g1 = 2.47, g2 = 2.42 and g3 = 1.78 (Σg2 = 15.1). These spectroscopic observations are indicative of a metal-
based electron in the dπ orbital for the [Fe(TPC)(1-MeIm)2]CF3SO3 (1) complex with a (dxy)2 (dxzdyz)3 ground
state at any temperature.
γ-spirolactone16 and a tyrosine as the proximal ligand.17
A
Introduction
heme d prosthetic group with the same configuration has also
been found in the crystal structure of Penicillium vitale
catalase.18 Evidence favoring coordination of a tyrosinate
proximal ligand to the chlorin iron of E. coli Hp II catalase was
previously proposed by Dawson et al.19
The essential objective of hemoprotein research is the elucid-
ation of the structural and electronic factors that control the
different functional properties of the active site heme group.
The nature of axial ligands that are ligated to the heme group is
the major determinant of reactivity. However, even in many
cases where imidazole serves as the axial ligand, wide variation
in reactivity is present as a result of small changes in orientation
or in the presence of a nearby residue. Thus, imidazole is one of
the most studied ligands in five- and six-coordinate derivatives
of iron porphyrins. This is largely due to the fact that physio-
logically relevant ligands provided by the protein include the
imidazole side chain of histidine which can be found in many
hemoproteins such as hemoglobins,1,2 cytochromes c,3 cyto-
chromes b4 and cytochromes f.5 Two limiting orientations of
the axial ligand planes have been implicated in the structures of
cytochromes having two axial imidazole ligands, either the
imidazole planes are oriented parallel to each other (cyto-
Iron chlorins are porphyrin-derived iron-containing pros-
thetic groups in which one of the peripheral double bonds of
the porphyrin ring has been reduced to yield a dihydropor-
phyrin. Although some investigations of the NMR and EPR
spectra of low-spin iron() complexes of reduced porphyrins
have been investigated by us20,21 and others,22–32 the nature
of the electronic ground state is not always clear and more
information is needed with these systems. Magnetic circular
dichroism spectroscopy has also been shown to be of great
utility in the identification of proximal and distal axial ligands
in chlorin-containing proteins.33,34 However, only a limited
number of iron chlorin complexes such as high-spin ferrous,35,36
high spin ferric31,37 (µ-oxo)bis[(tetraphenylchlorin)iron()],38
and low-spin ferric tetraphenylporphyrin20 species have been
investigated with X-ray crystallography. We now report the
first X-ray structure and 1H NMR analysis of the bis(1-
methylimidazole) adduct of ferric tetraphenylporphyrin, as a
low-spin complex. The purpose of this study is to extend the
coverage of iron chlorin models with physiological nitrogenous
ligands such as imidazole.
4
chrome b5 ) or the imidazole planes are oriented perpendicular
to each other (cytochrome c3 6 and cytochrome bc1 ).
7
In contrast, the electronic structure of iron chlorins still
represents a recently active and challenging area8 because iron
chlorins have been found as the prosthetic groups of a number
of heme proteins in recent years. Cytochrome bd oxidase is a
bacterial terminal oxidase that contains three cofactors: a low-
spin heme (b558), a high spin heme (b595) and a chlorin d.9–11
Whereas X-ray structures have been published for several heme-
copper cytochrome c oxidases,12 no crystal structure is available
yet for the cytochrome bd family. The molecular mechanism of
the enzyme action has been studied in much less detail13,14 than
the heme-copper oxidases and the nature of the axial ligand of
heme d is still unknown. Heme d has also been found in
catalases, such as hydroperoxidase II, from Escherichia coli
(E. coli).15 In contrast to cytochrome bd oxidase, the crystal
structure of catalase HP II from E. coli has been determined
showing a heme d prosthetic group with a cis-hydroxychlorin
Results and discussion
Preparation of compound 1
The synthesis of the [Fe(TPC)(1-MeIm)2]CF3SO3 compound is
achieved by displacement of coordinate triflate from Fe(TPC)-
CF3SO3 21 according to eqn. (1).
Fe(TPC)CF3SO3 ϩ 2(1-MeIm)
[Fe(TPC)(1-MeIm)2]CF3SO3 (1)
DOI: 10.1039/b204006a
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Table 1 Selected bond distances (Å) and angles (Њ) for [Fe(TPC)-
(1-MeIm)2]CF3SO3
Bond
Distance/Å
Bond
Distance/Å
Fe1–N1
Fe1–N2
Fe1–N3
Fe1–N4
Fe1–N5
2.005 (6)
2.016 (6)
1.971 (6)
2.032 (5)
1.958 (5)
Fe1–N7
C2–C3
C7–C8
C12–C13
C17–C18
2.002 (6)
1.320 (11)
1.444 (12)
1.390 (10)
1.408 (11)
Angle
Degrees
Angle
Degrees
N1–Fe1–N3 178.4 (3)
N3–Fe1–N5
N3–Fe1–N7
N4–Fe1–N5
N4–Fe1–N7
N5–Fe1–N7
91.2 (2)
88.9 (2)
90.4 (2)
89.4 (2)
179.7 (3)
N1–Fe1–N5
N1–Fe1–N7
89.8 (2)
90.1 (2)
N2–Fe1–N4 178.3 (2)
N2–Fe1–N5
N2–Fe1–N7
91.2 (2)
89.1 (2)
In solution, the complex has a green–brown color, as
reported for the bis(dimethylphenylphosphine) adduct,20 and
shows a visible spectrum with λmax at 417, 595 and 634 nm.
During the synthesis, the two major difficulties are the oxid-
ation of the chlorin ring to the porphyrin ring and a possible
autoreduction of the ferric state.
Crystal structure of [Fe(TPC)(1-MeIm)2]CF3SO3
The molecule is a six-coordinate iron with four nitrogen atoms
of the porphyrin and two nitrogen atoms of the axial ligands.
An ORTEP diagram of the complex is shown in Fig. 1, along
with the atom numbering scheme. The most interesting bond
distances and angles are summarized in Table 1.
Fig. 2 A, Formal diagram of the porphinato core in [Fe(TPC)-
(1-MeIm)2]CF3SO3 showing the relative orientations of the axial
ligands with each other and the Fe–Np vectors. B, Also displayed
in the diagram are the displacements of each atom, in units of 0.01,
from the best plane of the 24-atom porphinato core.
above and below the mean plane of the chlorin (maximum
displacement 0.15 (2) Å). Fig. 2B gives out of plane distances
for the atoms in the chlorin core from the mean chlorin plane.
Thus the conformation of the chlorin macrocycle can be
described as weakly distorted and indicates that the ground
state is largely (dxy)2(dxzdyz)3 (vide infra).
Fig. 1 Atom labels and perspective view for the cation 1.
A convenient measure of the orientation of imidazole ligands
in metalloporphyrin complexes is to use the dihedral angle ꢀ
between the imidazole plane and a plane perpendicular to the
porphinato core and passing through a porphinato nitrogen
atom.39,40 As shown in Fig. 2A, the two axial ligand planes are
coplanar with a unique ꢀ angle of 21.8Њ. This is different from
the analog porphyrin complex [Fe(TPP)(1-MeIm)2]ClO4 in
which the axial ligands form ꢀ angles of 22Њ and 32Њ with an
angle of 10Њ separating the ligand planes.41 ꢀ values between 0Њ
and 20Њ are however a common feature of six-coordinate
imidazole-ligated metalloporphyrins.42 Thus preferred orient-
ation of imidazole ligands in iron porphyrins has been largely
discussed by Scheidt group on the basis of analysis of many
X-ray structure determinations.40 Charge iterative extended
Hückel theory calculations on electronic effects for a large
group of representative systems indicate an orientational
preference in the M–N(imidazole) bond which favors eclipsed
orientation.
The C(7)–C(8) (1.444(12) Å) distance in the pyrroline ring is
longer than the usual values of the three remaining pyrroles
(average value of 1.373(10) Å) and reflects the sp3 hybridization
of the corresponding pyrroline atoms. Such a situation was
previously observed with three iron chlorins: the low-spin com-
plex [Fe(TPC)(PMe2Ph)2]CF3SO3 (C–C distance: 1.446 (16)
Å),20 the ferrous octaethylchlorin (OEC)Fe (C–C distance:
1.508(7) Å)36 and the µ-oxo complex [(TPC)Fe]2O (C–C
distance: 1.419(9) Å).38
The metal–nitrogen distance to the reduced pyrrole, N(2)
(2.016 (6) Å), and the nitrogen N(4) (2,014 (6) Å) are longer
than and the two remaining nitrogens: N(1) and N(3) (average
Fe–N distance: 1.988 (6) Å). These values are different to those
41
found for [Fe(TPP)(1-MeIm)2]ClO4 in which the four Fe–N
distances average to 1.981 (3) Å. Thus there is a core-hole
expansion of the macrocycle due to the reduced pyrrole. Such a
situation, but to a lesser extent, has been recently reported by
us20 with the comparison of the two complexes [Fe(TPC)-
(PMe2Ph)2]CF3SO3 and [Fe(TPP)(PMe2Ph)2]CF3SO3.43 It
The pyrrole and pyrroline atoms are only slightly displaced
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Table 2 Observed and isotropic shifts of [Fe(TPC)(1-MeIm)2]CF3SO3 1 (δ, CD2Cl2, ppm)
Proton chlorin
Ho
HoЈ
Hm
HmЈ
Hp
HpЈ
Hpyrro
Hpyr1
Hpyr2
Hpyr3
(∆H/H)a
(∆H/H)b
(∆H/H)iso
6.17
7.6
Ϫ1.43
6.17
7.8
Ϫ1.63
7.22
7.6
Ϫ0.38
7.11
7.6
Ϫ0.49
7.11
7.6
Ϫ0.49
6.91
7.6
Ϫ0.69
39.14
4.35
34.79
Ϫ1
7.6
Ϫ8.6
Ϫ10
8.2
Ϫ18.2
Ϫ35
7.6
Ϫ42.6
c
Proton ligand
H2
H4
H5
Me
(∆H/H)a
(∆H/H)
(∆H/H)iso
Ϫ5.73
Ϫ0.8
Ϫ4.9
1.78
0.4
1.3
3.11
4.0
Ϫ0.9
12.6
1.6
11
d
a Chemical shift of [Fe(TPC)(1-MeIm)2]CF3SO3 1 at 298 K with TMS as internal reference. b Chemical shift of [Fe(TPC)(PMe2Ph)2] at 298 K with
TMS as internal reference. c Isotropic shift of 1 with diamagnetic complex [Fe(TPC)(PMe2Ph)2] as reference. We used a medium value of 7.8 ppm for
the chemical shifts of the diamagnetic pyrroles since the relative assignment was not possible at this stage. d Isotropic shift of 1 with diamagnetic
ruthenium() mesoporphyrin dimethyl ester complex Ru(MPDME))(CO)(1-MeIm) as reference.48
should also be noted that the equatorial Fe–Np bonds that are
approximately perpendicular to the imidazole ring planes in
[Fe(TPP)(1-MeIm)2]ClO4 are significantly shorter than the set
that are approximately parallel to the imidazole plane, the
respective averaged values are 1.973 and 1.991 Å.41 This rhom-
bic effect which is due to the π-donating ability of the imidazole
ligand to the half-filled dyz orbital of the metal was also noted
for [Fe(TPP)(Him)2]Cl.44 With the [Fe(TPC)(1-MeIm)2]CF3SO3
complex, the expected rhombic distortion due to the reduced
ring results in an axial ligand orientation nearly along the Fe–N
(pyrroline) bond. This situation may result from competition
between the chlorin ring and imidazole ligand to π-donate to
the iron().
The axial Fe–N(5) and Fe–N(7) distances are 1.958 (5) and
2.002 (6) Å, respectively. Thus, the average axial Fe–N(Im)
distance of 1.9805 Å is slightly longer than in the iron() com-
plex of TPP containing the same ligand [Fe(TPP)(1-MeIm)2]-
ClO4 (1.974(6) Å)41 and is typical of distances observed
previously with unhindered imidazole derivatives.
The hyperfine shifts for symmetrical low-spin ferric por-
phyrins are known to consist of large contact shifts and smaller
upfield dipolar shifts due to the magnetic anisotropy. In chlorin,
the symmetry is lost but La Mar and coworkers have suggested
that such a situation is also highly probable with low-spin ferric
chlorins.26 It should also be underlined that spin density distri-
butions estimated using Hückel molecular orbital calculations
for [Fe(TPC)(ImH)2]ϩCl have been recently reported.32,47
Pyrrole. The spectrum of [Fe(TPC)(1-MeIm)2]CF3SO3
1 shows the pyrrole proton signals at Ϫ1.0, Ϫ10.0 and Ϫ35.0
ppm (298 K). This is quite different from the pyrrole proton
signals of two other low-spin Fe() chlorinates at ambient
temperature: [Fe(TPC)(PMe2Ph)2]CF3SO3 (0.66, 0.66 and
Ϫ57.8 ppm)20 and [Fe(QTPP)(Im)]ϩ (Ϫ12.2, Ϫ15.6 and Ϫ21.7
ppm, 293 K),31 but close to the pyrrole proton signals of
[Fe(TMC)(Im)2]Cl (Ϫ2.4, Ϫ12.3 and Ϫ47.1 ppm, 203 K).29
Pyrroline. For the saturated pyrroline ring, the protons are
expected to exhibit low-field π contact shifts.26 The observed
large low-field shift (δ = 39.1 ppm) for 1 agrees with an import-
ant π metal bonding involving a molecular orbital of the
chlorin derived either from the a1u orbital25 or from the 3eπ
orbital of a porphyrin.32 This contact shift is very similar to that
of the corresponding [Fe(TMC)(Im)2]Cl (δ = 38.3 ppm)29 and
not too far from those of pyropheophorbide a methylester
iron() (δ = 24 and 28 ppm).26 Since the contact shift has been
shown to arise predominantly from spin delocalization into
the bonding dxz and dyz orbitals,26 this result agrees with a
(dxy)2(dxz,dyz)3 electronic structure in this imidazole derivatives
(see below).
1H NMR spectroscopy
The 1H NMR spectrum of [Fe(TPC)(1-MeIm)2]CF3SO3 at
298 K is shown in Fig. 3. The peaks for the phenyl protons
Phenyl. In contrast to the pyrrole protons, the phenyl protons
show weak isotropic shifts which are found to be essentially
dipolar in origin. Thus a plot (∆H)iso vs. (3cos2 Ϫ 1)/r3 for all
protons is linear and confirms the quasi absence of contact
shift in this position.
Fig. 3 1H NMR spectrum of [Fe(TPC)(1-MeIm)2]CF3SO3 recorded at
283 K in CD2Cl2.
Ligand. The chemical shifts of the protons of the 1-Me
imidazole ligands of [Fe(TPP)(1-MeIm)2]Cl and the isotropic
shifts of the imidazole ligands of [Fe(TPP)(Im)2]Cl have been
reported.48 It has been found that the imidazole ligand shifts are
consistent with delocalization into the filled orbitals that have
large density on the bonding nitrogen.49 The hyperfine shifts,
obtained by referencing the observed shift to that of a corre-
sponding diamagnetic Ru() complex49,50 are summarized in
Table 2. The paramagnetic shifts of 4-H and 5-H are weak and
reflect the balance of a positive dipolar shift and a negative
contact shift. The shift of 2-H is at a stronger field (δ = Ϫ4 ppm)
due to more π delocalization at that position. In comparison
with the analogous complex with porphyrin, the effects are
similar but to a lesser extent in the chlorin case. This decrease
of the porphyrin ring are assigned completely by 2D COSY
spectra. For the imidazole ligands and the pyrroles, the relative
intensities and 2D COSY determine the assignment. The shifts
of the imidazole ligands are independent of the presence of
excess ligand, and hence axial ligand dissociation does not
appear to be significant at ambient temperature. Magnetic
measurements using the method of Evans45,46 were made for
0.03 M CD2Cl2 solutions of 1 at 297 K, employing Me4Si as
the reference. The solution magnetic moment (µ = 1.93 µB) is
compatible with a low-spin state, S = 1/2. The hyperfine shifts,
obtained by referencing the observed shift to that of the corre-
20
sponding diamagnetic complex Fe(TPC)(PPh(Me)2)2
summarized in Table 2.
are
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is probably due to a larger contribution of iron chlorin than
iron porphyrin. Thus the same conclusion can be reached:
imidazoles interact with low-spin iron() as π donors and the
mechanism of spin delocalization is 1-methylimidazole towards
Fe π bonding. These results also confirm the (dxy)2 (dxz, dyz)3
ground state, both in porphyrin and chlorin complexes
Analysis of the curve in the Curie plot was made for
the [Fe(TPC)(1-MeIm)2]CF3SO3 complex. The temperature
dependence of the chemical shifts of the protons in CD2Cl2 are
shown in Fig. 4. A magnetically simple molecule is expected to
absolute values of the components of the g-tensors and not
their orientation with respect to the molecular frame. Since, it
was found recently32 that the orientation and electronic ground
states are not necessarily those expected on the basis of the
Taylor analysis,53 which assumes that the rhombicity must
be less than 2/3, our proposition cannot be considered as defini-
tive. However the EPR results, strongly suggest a (dxy)2 (dxz, dyz)3
ground state. Thus the EPR spectrum of CH2Cl2 frozen
solutions of complex 1 (Fig. 5) shows EPR signals with the
Fig. 5 EPR spectrum of [Fe(TPC)(1-MeIm)2]CF3SO3 in a CH2Cl2
glass, recorded at 4 K.
principal g-values g1 = 2.47, g2 = 2.42 and g3 = 1.78 (Σg2 = 15.1).
The electronic structure of 1 is rhombic and is described
in terms of crystal field parameters as rhombic (∆/λ) and
tetragonal (V/λ) components normalized to the spin-orbit
coupling constant (λ). These values can be determined from the
principal EPR g values using the expressions given by Taylor.53
Using the values of complex 1 yields V/λ = 3.8 and ∆/λ = 2.3
(V/∆ = 1.6) with the largest magnitude g value assigned to the
heme normal independent of the value of V/∆. The principal
g values for a similar complex, [Fe(TPC)(Im)2]Cl are g1 = 2.49,
g2 = 2.39 and g3 = 1.75 (Σg2 = 15.0).32 In contrast, for [Fe(TPC)-
(CN-t-Bu)2]Cl, where Σg2 = 13.1 is much lower, a considerable
amount of orbital angular momentum is quenched in this
complex according to a (dxz, dyz)4(dxy)1 ground state.21 This
interpretation is also supported by a recent EPR results on
[Fe(TPC)(Im)2]Cl reported by Walker et al. showing that the
highest g value is gz in this complex with a (dxy)2 (dxz, dyz)3
ground state.32
Geiger et al. have suggested that magnetic properties in
iron() porphyrins can depend on the rotational orientation
of the axial ligands with respect to the equatorial M–Np bonds
of the porphyrin.42 Walker et al. have also studied the possible
effect of the relative axial ligand orientation on the EPR and
1H NMR of bis(imidazole)iron() porphyrinates as models of
cytochromes b.54 It is reported that a perpendicular orientation
of the two axial ligands leads to an unusual EPR spectrum
which was called “large gmax” (g value > 3.3).55 In contrast, the
EPR spectrum of complex 1 in solution agrees with a parallel
orientation which is also observed in the X-ray structure.
Fig. 4 Curie plot of the chemical shifts vs. reciprocal temperature of
[Fe(TPC)(1-MeIm)2]CF3SO3 in CD2Cl2. A: phenyl protons; B: pyrrole
and pyrroline protons.
follow Curie-law behavior in that a plot of the chemical shifts
vs. 1/T is linear with an intercept equal to the resonance in the
diamagnetic complex. Plots of ortho, meta and para signals
of meso-aryl protons of the chlorin ring are reasonably
linear which intercepts at 8.03, 7.4, and 7.34 ppm respectively
(Fig. 4A). However these protons show only small temperature
dependence, consistent with a weak spin density on the meso
position. For the pyrrole resonances, the chemical shifts vary
linearly with 1/T , but the extrapolated lines do not pass
through the diamagnetic value at 1/T = 0 Fig. 4B).
EPR spectroscopy
Among the heme proteins, the paramagnetic states of iron
are particularly amenable to spectroscopic investigations by
electron paramagnetic resonance (EPR).51 Thus EPR spectro-
scopy has been used for classifying low-spin ferriheme proteins
and model porphyrin complexes on the basis of a crystal field
analysis developed by Griffith.52 For low-spin ferrihemes,
Blumberg and Peisach used the tetragonality ∆/λ and rhomb-
icity V/∆ parameters which are obtained from the three g-values
of the typically rhombic EPR spectra with λ being the spin-
orbit coupling.51 However, continuous wave EPR yields only
Conclusion
In conclusion, these spectroscopic observations are indicative
of a metal-based electron in the dπ orbitals of the [Fe(TPC)-
(1-MeIm)2]CF3SO3 complex at any temperature. Thus the
change in ground state of low-spin Fe() from the usual (dxy)2
(dxz,dyz)3 to the unusual (dxz,dyz)4 (dxy)1 electron configuration
which was previously suggested to occur from porphyrin to
chlorin macrocycles51 is not observed with 1-methylimidazole
ligands. However, the unusual (dxz,dyz)4 (dxy)1 electron configur-
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J. Chem. Soc., Dalton Trans., 2002, 4011–4016

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Table 3 Crystallographic data for [Fe(TPC)(1-MeIm)2]CF3SO3
ation of low-spin Fe() is possible both with porphyrin
and chlorin macrocycles but seems largely related to the π-
acceptor properties56 of the ligands such as isocyanide57–60 and
phosphonite.61
Empirical formula
FW
FeC53H42N8F3O3S
984.04
Crystal system
Space group
a/Å
b/Å
c/Å
α/deg
β/deg
Triclinic
P1
9.1730 (3)
10.6674 (4)
13.3392 (5)
80.497 (2)
79.141 (2)
75.696 (2)
1232.48 (8)
1
Experimental
General information
As a precaution against the formation of the µ-oxo dimer
[Fe(TPC)]2O,38,62 all reactions were carried out in dried solvents
in Schlenk tubes under an Ar atmosphere. Solvents were
distilled from appropriate drying agents and stored under
γ/deg
V/Å3
Z
ρcalcd/g cmϪ3
µ/cmϪ1
T /K
1.326
4.03
150
1
argon. H NMR spectra were recorded on a Bruker AC 300P
spectrometer in CD2Cl2 or CDCl3 at 300 MHz. Tetramethyl-
silane was used as the internal reference. The temperatures
are given within 1 K. EPR spectra were recorded in CH2Cl2 on
a Bruker EMX 8/2,7 spectrometer operating at X-band fre-
quencies. Samples were cooled to 4.2 K in a stream of helium
gas in frozen CH2Cl2, the temperature of which was controlled
by an Oxford Instruments ESR 900 cryostat. Visible spectra
were measured on a Uvikon 941 spectrometer in CH2Cl2.
Rw
Final R
0.194
0.068
observations with I > 2.0σ(I); calc w = 1/[σ2(Fo)2 ϩ (0.159P)2 ϩ
1.58P] where P = (Fo2 ϩ 2 Fc2)/3 with the resulting R = 0.068, Rw
= 0.194 and Sw = 1.059 (residual ∆ρ < 1.51 eAϪ3). Atomic
scattering factors were from the International Tables for
X-ray Crystallography.67 ORTEP views were realized with
PLATON98.68
CCDC reference number 184540.
See http://www.rsc.org/suppdata/dt/b2/b204006a/ for crystal-
lographic data in CIF or other electronic format.
Reagents
The following iron chlorins were prepared by literature
methods: Fe(TPC)Cl63 and Fe(TPC)CF3SO3.21 1-Methylimid-
azole is commercially available. Abbreviations used: TPC = 7,8-
dihydro-5,10,15,20-tetraphenylporphyrin dianion (tetraphenyl-
chlorin), TMC = 7,8-dihydro-5,10,15,20-tetra(2,4,6-trimethyl-
References
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quinoxalinotetraphenylporphyrin, TPP
phenylporphyrin dianion.
= 5,10,15,20-tetra-
Synthesis
[Fe(TPC)(1-MeIm)2]CF3SO3 1. To a solution of 0.1 g (0.12
mmol) of [Fe(TPC)] CF3SO3 in 5 ml of dichloromethane was
added 2.5 equiv. (13 µl) of 1-methylimidazole by a syringe
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CF3SO3
The X-ray study was carried out on a NONIUS Kappa CCD
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